The present invention relates to a method and an apparatus for breaking up and separating waste glass to obtain cullet.
Recycled waste glass contains caps and the like of glass bottles and may further contain empty bottles for beverages. In recent years, many of caps are made of aluminum, while some are made of iron, synthetic resin, cork, etc. Empty cans are generally aluminum and iron cans. When waste glass containing such extraneous matter is used as cullet, the glass product obtained contains bubbles and unmelted substances, i.e. so-called "stones," and involves changes in color or transparency due to the presence of the extraneous matter. These objections reduce the strength and appearance of the product, seriously impairing commercial value of the product.
Accordingly the extraneous matter must be removed to the greatest possible extent. However, the extraneous matter varies greatly in shape and properties. Moreover, regardless of whether the waste glass has been fractured or not, some kinds of extraneous matter may not differ from the waste glass in shape, size or specific gravity. Thus the undesirable matter is not readily separable by the conventional methods such as screening, washing with water, sink and float separation, etc., with the exception of magnetic materials which are magnetically separable. In fact, the conventional methods give very low yields. For this reason, for the preparation of cullet, extraneous matter is usually removed from the waste glass by manually roughly breaking waste glass, separating off soil, sand, mud and like fine particles by screening, washing the oversize pieces with water to remove paper, cork and synthetic resin extraneous materials, and further manually removing caps, empty cans and other extraneous pieces while magnetically separating off magnetic material. However, the usual method involves the cumbersome and inefficient manual separation step and still permits a large amount of extraneous matter to remain in the waste glass.
On the other hand, because finely divided glass produces bubbles when melted in the furnace and because of the necessity of assuring effective and efficient operation of the optical color separator (such as SOTEX 31) used to obtain good cullet, glass pieces must have sizes within a specified range (e.g. -20 to +5 mm). For this purpose, waste glass in conventionally broken up with use of jaw crushers and impeller breakers for ore and stone, instead of resorting to an inefficient manual breaking procedure. However the operation with use of such crushers tends to cause abrasion and compression, consequently impairing the quality of cullet or reducing the yield.